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[QUOTE]Originally posted by DD'eDeN: [QB] 5.3ma LCA Human/Chimp split per gut bacteria Hominid superorganisms Julia Segre & Nick Salafsky 2016 Science 353:350-1 doi 10.1126/science.aag2788 Mutualistic symbiotic relationships are those in which both spp benefit, e.g. the vivid colors of coral reefs come from symbiotic algae that provide their living coral hosts with nutrients & O2 through photosynthesis, in exchange for protection. A similar mutualistic relationship exists between gut-dwelling bacteria & their animal hosts. But to what degree has symbiosis shaped host-microbial interactions & coevolution? Moeller cs (p.380) show that gut bacterial strains co-speciated with hominids (apes & humans) over the past 15 Ma. This sets the stage for exploring the evolutionary processes that underlie the symbiotic relationship between hominids & their gut-dwelling microbes. Moeller cs obtained fecal samples from wild Pan troglodytes (Tanzania), P.paniscus (Dem.Rep.Congo), G.gorilla (Cameroon) & H.sapiens (US). They use DNA gyrase subunit B (gyrB, a single-copy protein-coding gene in bacterial genomes that evolves at a moderate rate) as a marker to assess strain diversity of Bifido-bacteriaceae (Biff.), Bacteroidaceae (Bact.) & Lachnospiraceae (Lach.) in the gut of humans, chimpanzees, bonobos & gorillas. This rel.constant gyrB molecular clock data allows them to compare the timing of speciation of gut bacterial communities with the known speciation patterns of their hominid hosts. For different Bact.spp, Moeller cs explore the phylogenetic relatedness of closely related strains from the feces of the hominids. Taking the most commonly related gyrB-sequence from each hominid, the authors calculate the LCA: bonobo- & chimp-associated strains are most closely related to each other, and together form a sister-clade to the gorilla & human clades. This phylogenetic relationship among hominid-associated Bact.strains mirrors the host evolutionary topology. For most genera of Bact.e, the dominant pattern of diversification is hominid-microbial parallel co-speciation, but the authors also report small anomalies, e.g. some Bact.lineages are absent from either humans or gorillas, representing lost microbial diversity. Biff.strain phylogeny +-mirrors that seen for Bact.lineages, but Lach.strains show evidence for transfer between host spp, perhaps because Lachn. can survive as spores (can more readily disperse & transfer among host spp). Thus, different evolutionary pressures & forces may shape both host & microbial community members. Evidence for cospeciation Moeller cs demonstrate that Bact. & Biff.strains (shown as hues of the same color) co-speciated with their hosts. This suggests that symbiosis may be an evolutionary force. To corroborate their findings, Moeller cs also re-analyzed ribosomal sequence data from chimps & gorillas that live together in regions of Cameroon. They found no sequences that were 100 % identical, suggesting that distinct strains co-evolved with their hosts. To explore if geographic separation might foster diversification within a species, they show that bacterial lineages differ between humans in Malawi & US. Based solely on the sequence divergence of gut bacteria, Moeller cs date the H/P split at 5.3 Ma, in agreement with estimates based on host mtDNA, but slightly later than estimates based on nuclear genomes. They calculate the H/G split at 15.6 Ma, older than estimates based on mtDNA, but within the range of estimates based on nuclear genomes. [/QB][/QUOTE]
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